[Widgets] Support theming

[tracy-french]

To make it possible to get an iot-app-kit widget to match the styling of the consuming application, we will expose a hook-based theming API.

Below is the expected API, which should be exported from `@iot-app-kit/react-components';

import { type Theme } from '@cloudscape-design/components/theming';

/** Collection of Cloudscape design tokens supported for theming. */
type SupportedCloudscapeDesignTokens = Pick<Theme['tokens'], 'fontFamilyBase'>;
/** Collection of design tokens supported for theming. */
type Tokens = SupportedCloudscapeDesignTokens;

export interface UseThemeOptions {
  /**
   * Specifies the mode (i.e., color scheme) of the components.
   * 
   * @defaultValue `light`
   */
  mode?: 'light' | 'dark';
  /**
   * Specifies design token overrides to change the styling of components.
   */
  tokens?: Tokens;
}

/**
 * Use to set the theme of `iot-app-kit` components.
 *
 * @experimental
 * This API is experimental, is not completely functional, and is subject to 
 * breaking changes. Until stabilized, many components will not see styling 
 * changes. Do not use in production.
 */
export function useTheme({ mode = 'light', tokens }: UseThemeOptions): void {
  // implementation
}

The implementation should use Cloudscape mechanism for setting mode and theme. Please read the follow documents to understand how Cloudscape does this:

• https://cloudscape.design/foundation/visual-foundation/visual-modes/
• https://cloudscape.design/foundation/visual-foundation/theming/

The implementation should depend on the following imports:

import { applyMode, Mode } from '@cloudscape-design/global-styles';
import { applyTheme, type Theme } from '@cloudscape-design/components/theming';

For the initial implementation, we will only expose a single token (fontFamilyBase) and the mode selection. We are only exposing a little at a time as there is additional implementation on our side to ensure all custom components are using the appropriate Cloudscape design tokens, where applicable.

The font family theme setting should be fully functional. The mode setting should use applyMode, but making sure it works effectively will be completed in separate changes.

Acceptance criteria

Beta Give feedback

1. useTheme and UseThemeOptions are exported from @iot-app-kit/react-components.
2. useTheme supports setting the fontFamilyBase design token. All components in react-components should use the custom font family, as well as the resource explorer in the dashboard (applyMode and applyTheme change global styles, so it does not matter that the resource explorer is not currently in the same package).
3. useTheme supports setting light mode.
4. useTheme supports setting dark mode.